U.S. patent number 4,379,665 [Application Number 06/209,600] was granted by the patent office on 1983-04-12 for insulation stripper for coaxial cable.
This patent grant is currently assigned to Lemco Tool Corporation. Invention is credited to Homer Hendershot, Charles M. Storrs.
United States Patent |
4,379,665 |
Hendershot , et al. |
April 12, 1983 |
Insulation stripper for coaxial cable
Abstract
A stripping tool for removing annular insulation from between
the conductors of a coaxial cable includes a stripping bit having a
pair of longitudinally extending flutes, cutting edges at the head
of the bit, a stop shoulder remote from the cutting edges having an
outer diameter greater than the diameter of the head and a recessed
connecting portion between the head and shoulder having a diameter
less than the diameter of the head.
Inventors: |
Hendershot; Homer (Cogan
Station, PA), Storrs; Charles M. (Williamsport, PA) |
Assignee: |
Lemco Tool Corporation (Cogan
Station, PA)
|
Family
ID: |
22779444 |
Appl.
No.: |
06/209,600 |
Filed: |
November 24, 1980 |
Current U.S.
Class: |
408/204;
29/426.4; 30/90.1 |
Current CPC
Class: |
B23B
51/0406 (20130101); H02G 1/1226 (20130101); B23B
2270/22 (20130101); Y10T 408/895 (20150115); Y10T
29/49821 (20150115) |
Current International
Class: |
B23B
51/04 (20060101); H02G 1/12 (20060101); B23B
051/04 () |
Field of
Search: |
;408/203.5,204,205,206,207,67,202 ;81/9.5R,9.5C |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Advertisement Disclosing Cable Dielectric Coring Tool-Ben Hughes
Communication Co..
|
Primary Examiner: Vlachos; Leonidas
Attorney, Agent or Firm: Hooker; Thomas
Claims
What I claim my invention is:
1. An insulation stripping tool for coaxial cable having a body
with cable alignment means at one end and a stripping bit at the
other end axially aligned with the means, the bit including a
cutting end adjacent to the means with an insulation cutting edge
and a sleeve stop surface away from the means, wherein the
improvement comprises an axial bore extending into the bit from the
cutting end and an insulation carrying flute on the surface of the
bit extending longitudinally along the bit from the cutting edge
past the sleeve stop surface, the cutting edge facing in the
direction of stripping rotation of the tool, said flute including a
bottom surface extending from one side of the bit past the bit axis
and a side wall extending from the bottom wall to the surface of
the bit, the side wall including a section extending longitudinally
along the bit and a curved section at the cutting end of the bit
running from one end of the longitudinal section to the cutting
edge whereby upon stripping rotation of the tool and feeding of the
bit into an end of a coaxial cable held by the means the cutting
edge severs a strip of insulation from between the central
conductor and the surrounding conductive sheath and the flute
carries the strip away from the cutting edge, axially along the bit
and outwardly the cable without jamming while the central conductor
is fed into said bore.
2. An insulation stripping tool as in claim 1 wherein the diameter
of the axial bore is increased away from the cutting end of the
bit.
3. An insulation stripping tool as in claim 1 wherein the bit
includes a cutting head carrying the edge, a shank and a connecting
portion joining the head and shank, the outer surface of the head
being shaped to conform to the inner surface of the cable outer
sheath and the connecting portion being smaller than the head so as
to collect an insulation layer left on the outer sheath following
stripping by the edge, the end of the shank adjacent the connecting
portion defining the stop surface.
4. An insulation stripping tool as in claim 1 wherein the bit
includes a cylindrical cutting head carrying the edge, a
cylindrical shank and a cylindrical connecting portion between the
shank and head, the diameter of the head being equal or slightly
less than the interior diameter of the outer sheath of coaxial
cable stripped by the tool, the diameter of the connecting portion
being less than the diameter of the head and the diameter of the
shank being greater than the diameter of the head, and a stop
shoulder between the connecting portion and shank defining said
stop surface.
5. An insulation stripping tool as in claim 1 wherein the bit
includes a second cutting edge like said cutting edge and a second
flute like said flute, the cutting edges are diametrically opposed
across the cutting end of the bit and face in the same
circumferential direction, and the flutes extending longitudinally
past the stop surface on opposite sides of the bit.
6. An insulation stripping tool as in claim 5 wherein the flute
bottom surfaces are essentially tangent to the first portion of the
bore.
7. An insulation stripping tool as in claim 6 where the second
portion of the bore intersects the bottom surfaces to define a pair
of longitudinal slits.
8. An insulation stripping tool for a coaxial cable comprising a
body, a cable alignment bushing at one end of the body, a holder
for a bit at the other end of the body, ribs joining the ends of
the body, a stripping bit secured within the holder in axial
alignment with the bushing including a cutting end adjacent the
bushing, a circumferential sheath stop surface away from the
bushing wherein the improvement includes a cylindrical head at the
cutting end of the bit having a first diameter, a connecting
portion between the head and the stop surface having a diameter
less than the diameter of the head, the head including a pair of
opposed cutting edges facing the same circumferential direction, a
pair of longitudinal flutes formed in and extending along the
length of the bit, each flute including a first wall having a
longitudinal portion extending past the stop surface at one end and
a curved portion at the other end extending to the edge, and an
axial bore extending into the bit from the cutting end.
9. An insulation stripping tool as in claim 8 wherein each flute
includes a flat bottom surface extending from one side of the bit
past the bit axis and joining said first wall.
10. An insulation stripping tool as in claim 8 wherein said bore
includes a first portion at the cutting head and a second portion
remote from the cutting head, the diameter of said first portion
being less than the diameter of said second portion.
Description
The invention relates to tools for stripping insulation from
between the outer and inner conductors of a coaxial cable of the
type used to transmit television, FM or other electrical signals.
These cables have a relatively delicate outer sheath and an inner
conductor core with the space between the core and the sheath
filled by a foamed-plastic dielectric material. In order to attach
the electrical connector to the end of the cable, it is necessary
to strip or core out a portion of the insulation within the cable
to allow a cylindrical portion of the connector to extend under the
outer sheath so that the sheath can be subsequently clamped against
the portion to form the desired electrical connection. The center
conductor extends beyond the stripped sheath and is clamped to
another portion of the connector.
Conventionally, coaxial cables of this type have been stripped or
cored out using an auger-type tool similar to the tool of Ober et
al U.S. Pat. No. 1,567,812. The tool now used to strip away
insulation from modern coaxial cables includes a handle supporting
a stripping bit with a cable aligning bushing axially spaced from
the lead end of the bit. The bit includes a helical single flute
having a single cutting edge at the lead end. The flute winds
around a cylindrical hole which receives the central conductor of
the cable. The cable to be stripped is piloted into the alignment
bushing and held while the tool is rotated so that the cutting edge
feeds into the insulation. The tool is self-feeding. Rotation
without a driving force feeds the cutter into the insulation to cut
away a single insulation strip. This strip is channeled into the
relatively narrow flute. The high friction between the insulation
and the sides of the flute jams the insulation in place so that
during a single coring operation it may be necessary to retract the
tool a number of times and manually poke the insulation out from
the flute. This is a laborious and time-consuming operation.
The conventional tool includes a stop shoulder in the path of the
cable sheath. When coring has been completed to the proper depth,
the end of the sheath bottoms on the shoulder. Because the
conventional tool is self-feeding and does not signal bottoming of
the sheath, there is a tendency for the operator to continue
rotating the tool after the sheath bottoms on the shoulder, thereby
deforming the sheath radially outwardly of the shoulder. Such a
deformed sheath cannot be readily withdrawn from the sliding fit
bushing without further injury to the cable. In some cases, the
sheath may be pulled out of the bushing without visible harm. The
sheath, however, may be stressed sufficiently that future thermal
loading, wind vibration and the like could completely break the
sheath resulting in the cable pulling out from the connector. In
some cases, it may be necessary to trim off the newly stripped
sheath in order to remove the expanded end from the tool. This
foreshortens the cable and requires restripping, both of which are
highly undesirable.
The conventional stripping tool removes the insulation from the
outer surface of the inner conductor so that any buckling of the
inner conductor during or after the crimping operation risks the
possibility of the inner conductor contacting the inner connector
collar and shorting out the cable. This type of short is difficult
to locate in a cable. In order to fix the short, the old connector
must be removed, the cable restripped and a new connector must be
attached.
The conventional stripping tool also leaves a thin layer of
insulating material on the inner surface of the outer sheath,
requiring the operator to strip away the insulation layer with a
pen knife or similar device after the stripping tool has been
withdrawn from the cable. This manual step slows down stripping and
subjects the stripped cable end to forces likely to injure the
relatively delicate exposed conductors.
The improved stripping tool of the present invention strips away
the insulation from between coaxial cable conductors without
jamming or overfeeding to deform the outer conductor. The stripping
operation is hand-fed and automatically ends when the outer sheath
bottoms on the stop shoulder and the cutting edges are held by the
shoulder from stripping further into the cable. Stripping does not
outwardly flare the sheath. Manual overfeeding is avoided by a
torque-reduction signal when the outer sheath bottoms and by visual
inspection indicating bottoming. Further rotation of the tool after
bottoming spins the tool with respect to the cable and does not
strip additional insulation.
The insulation is cut away by a pair of opposed cutting edges and
flows along a pair of opposed longitudinal flutes outwardly of the
tool and cable without jamming. The cable is stripped in a
continuous operation. The tool need not be withdrawn during the
stripping to clear the stripped insulation. The stripped coaxial
cable is readily withdrawn from the alignment bushing without
injury to the delicate exposed sheath.
During stripping, the stripping bit removes the insulation from the
inside of the outer cable sheath to bare that surface for
subsequent formation of an electrical connector with a connector
mounted in the end of the cable. The bit leaves a thin insulating
layer on the inner conductor to assure that any bowing of the inner
conductor during crimping of the connector does not short-circuit
the inner conductor to the outer conductor through the
connector.
Other objects and features of the invention will become apparent as
the description proceeds, especially when taken in conjunction with
the accompanying drawings illustrating the invention, of which
there is one sheet and one embodiment.
IN THE DRAWINGS:
FIG. 1 is a partially-broken away side view of an insulation
stripper according to the invention;
FIG. 2 is an enlarged view of a portion of FIG. 1;
FIG. 3 is a side view of a bit used in the stripper;
FIG. 4 is a sectional view taken along the line of 4--4 of FIG. 3;
and
FIG. 5 illustrates the stripping operation.
Insulation stripping tool 10 includes a body 12 having an axial
bore 14 at one end and an axially aligned cable support bushing 16
at the opposite end. The body may be formed of a suitable material.
If formed of a conductive material, an insulating sleeve 18 may be
provided in bushing 16. Alternatively, the body may be coated with
an insulating material. Body base 20 and bushing 16 are connected
by a pair of ribs 22 located outwardly of the bore and bushing to
define an enlarged opening 24. A pair of handles 26 extend from
opposite sides of the base 20 and facilitate manual rotation of the
stripper.
Insulation stripper bit 28, shown in FIGS. 3 and 4, includes a
cylindrical shank 30 having a sliding fit within bore 14. Suitable
means (not illustrated) secure the bit within the bore for rotation
with the body. As shown in FIG. 1, the bit extends from base 20
across opening 24 nearly to bushing 16.
The bit includes a cylindrical head 32 having a lead end defined by
a pair of like flat surfaces 34 intersecting at a shallow angle on
a bit diameter. The diameter of head 32 is slightly less than the
nominal internal diameter of the outer sheath of the coaxial cable
stripped by the tool. The head is joined to the shank by a
cylindrical connecting portion 36 having a diameter less than the
diameter of the head. The diameter of the shank 30 is greater than
the inside diameter of the cable sheath and preferably equal or
greater than the outer diameter of the cable. Shoulders 38 and 40
join the ends of connecting portion 36 and head 32 and shank 30,
respectively.
The bit 28 includes a pair of like longitudinally extending flutes
42, each formed from a cutout in the bit and including a flat
bottom surface 44 extending from one side of the bit past the bit
axis 46 to a perpendicular flute side wall 48 extending back to the
bit surface. See FIG. 4. Surfaces 44 are parallel. The flutes 42
extend from head 32 past shoulder 40 and into the shank 30. The
forward end of each wall 48 curves toward the bit axis 46 at 50 to
reduce the metal beneath surface 34 and form a cutting edge 52.
Edges 52 face in the direction of stripping rotation of tool 10 and
may lie on a common bit diameter. See FIG. 4. The inner end of each
side wall 48 extends into the shank 30, around a curve 54 and
thence to the side of the bit. Each flute 42 extends into
connecting portion 36.
Axial bore 56 extends through the head 32 and joins a large
diameter axial bore 58 extending from shoulder 60 at the end of
bore 56 to the end of the bit in base 20. Bore 58 extends nearly to
head 32. Bore 58 intersects bottom walls 44 to form slits 59. As
illustrated in FIG. 4, the flute bottom surfaces 44 are nearly
tangent to bore 56.
Insulating stripper tool 10 is used to remove an end portion of the
annular dielectric insulation separating the electrically
conductive outer sheath from the axial conductor of a coaxial
transmission cable. While the tool is primarily adapted for
stripping insulation from cables of the type used to transmit
television signals, it may be used to strip insulation from other
types of cables.
Coaxial cable 70 includes an outer electrically conductive sheath
72 and an inner axial conductor 74. The sheath 72 may be a thin
walled aluminum tube formed by an extrusion process or from a sheet
of aluminum welded into a cylindrical configuration. The inner
conductor may be formed of a suitable conductive material.
Dielectric insulation 76 occupies the annular space between the
sheath 72 and conductor 74. This insulation is conventionally a
foamed plastic material having sufficient strength to locate the
conductor 74 in the center of the cable and to provide the desired
electrical separation or independence between the conductors.
Cable 70 transmits signals from a signal source to a signal
receptor. In the case of CATV systems, the cables carry television
transmission signals from signal sources to the customer through a
series of splices, amplifiers, splitters and other elements
dependent upon the design of the transmission system. In order to
transmit a signal into or out of a length of cable 70, it is
necessary to attach a connector to each end of the cable. The cable
end is prepared for receiving a connector by severing the
insulation and outer sheath from an end to expose a portion of the
inner conductor beyond the sheath and then stripping or coring out
the insulation between the sheath and conductor for a distance into
the cable sufficient to receive an annular portion of the
connector. An electrical connection is formed between the connector
and sheath by forcing the sheath against the annular member. An
electrical connection is formed with the central conductor by a
suitable clamping or crimp connection.
Tool 10 strips or cores out the insulation at the end of the cable
preparatory to attaching the connector. Following trimming back of
the sheath and insulation to expose end 78 of the inner conductor,
the end of the cable is piloted into the center opening of bushing
16 so that the cable is axially oriented with respect to the tool
and conductor end 78 extends into bore 56. The diameter of the bore
56 is greater than the diameter of the conductor. Further extension
of the cable into the bushing bottoms the bit end surfaces 34 on
the end of the insulation. The diameter of bit head 32 is slightly
less than the interior diameter of the sheath 72. Rotation of the
tool in the direction of arrow 80 shown in FIG. 5 while an axial
force in the direction of arrow 82 is applied to the tool feeds the
cutting edges 52 into the insulation to sever a pair of
diametrically opposed strips 84 from the insulation. With continued
rotation, these strips are forced along wall 48 away from the
cutting edges 52. Ultimately, the strips are guided along the
flutes 42 beyond shoulder 40 and are ejected outwardly of the bit
and tool through opening 24. The flutes guide the strips beyond the
end 86 of sheath 72 to avoid any possible jams during
stripping.
Rotation of the tool to cut away insulating strips 84 removes the
main body of the insulation within the cable leaving a thin layer
of insulation 88 surrounding the central conductor. The frictional
engagement between this remaining insulation layer and the bit is
reduced by the increased diameter of bore 58. Insulation 88 does
not engage the sides of bore 58, with the result a low torque is
required to rotate the tool during coring. This feature assures a
steady maximum torque is required during coring, rather than a
torque increasing with the depth of the coring operation. The
constant coring torque or "feel" enables the operator to readily
discern when the sheath has bottomed and the cable has been fully
cored.
The diameter of head 32 is slightly less than the nominal interior
diameter of the sheath 72 so that during coring a slight dielectric
film may be left on the inside of the sheath. Bit 28 automatically
removes this layer during coring and collects the layer in the
flutes 42 and the recess at connecting portion 36. When coring is
completed and the tool is removed from the cable, the interior
surface of the conductor 72 is free of insulation and ready to
receive the connector.
FIG. 5 illustrates a partially cored cable. Further rotation of the
tool with respect to the cable cuts away additional insulation to
deepen the cored end of the cable and move sheath end 86 toward
shoulder 40. Engagement between the sheath and shoulder bottoms the
tool to prevent further feeding of the edges 52 into the insulation
and reduces the torque required to rotate the tool. The reduced
torque is readily sensed by the operator as a signal that the
coring operation is completed and the tool may be withdrawn from
the cable.
Conventional coring tools having a single spiral cutter are
self-feeding so that once the coring operation has been initiated
rotation of the tool with respect to the cable feeds the cutting
edge into the insulation and draws the cutter into the cable. The
conventional tool does not provide the signal indicating the cable
has been cored to the desired depth and the sheath has bottomed on
a stop shoulder. Further rotation of such a tool after bottoming
continues to draw the cable into the tool and deforms the end of
the relatively delicate outer sheath radially outwardly at the
stop. The deformation in the sheath prevents withdrawal of the
cable from the alignment bushing. The deformed cable must be either
"jerked" out from the bushing or the deformed end of the sheath
must be cut off, the center conductor trimmed and the shortened
cable again cored. Shortening of the cable causes a number of
problems, particularly where the cable is originally cut to its
desired length. The cable may have been already strung and may have
to be spliced to provide additional length to permit the connector
to mate with another circuit element, such as an amplifier or an
additional length of cable. Such splices degrade the quality of the
signal transmitted through the cable. There are additional labor
costs associated with recoring or splicing the cable.
Sometimes it is possible to pull a slightly flared cable from an
alignment bush. This disengagement frequently requires hard pulling
and twisting of the cable relative to the tool. While the slightly
deformed cable once removed from the tool may appear to be
structurally sound, frequently the outer sheath has been severely
weakened by the withdrawal process and in many cases such sheaths
break or pop off thereby destroying the integrity of the cable and
frequently breaking the cable away from the attached electrical
connector. These problems are eliminated by use of the present tool
because the cutting edges are not self-feeding and the tool
provides a signal to the operator indicating when the coring
operation has been completed.
Tool 10 cores out a cable in a continuous rotary operation
commencing from first engagement between the cutting edges 52 and
insulation and continuing until the end of the sheath 86 bottoms on
shoulder 40 thereby preventing the cutting edges from severing
further insulation from the cable. The cutaway strips 84 are
smoothly guided down the longitudinal flutes and outwardly of the
bit during coring. The area through which the strips are guided is
defined by the flute surface and the interior surface of the outer
conductor sheath 72 is greater than the area of the strips so that
the foamed, flexible strips do not bind or jam within the flutes
and the coring operation is continuous until the sheath
bottoms.
In the drawings, bit 28 is held in a hand-rotated body 12.
Alternatively, the bit may be mounted in a body having an alignment
bushing similar to that of the tool but with a shank adapted to be
secured in the chuck of an electric drill or similar device. In
this way, the bit and body are rotated by a mechanical drive rather
than by hand. The coring operation using this tool is performed in
the same way as described in connection with the hand-held tool
10.
While we have illustrated and described a preferred embodiment of
our invention, it is understood that this is capable of
modification, and we therefore do not wish to be limited to the
precise details set forth, but desire to avail ourselves of such
changes and alterations as fall within the purview of the following
claims.
* * * * *